Bonded fibrous materials and method for making them

ABSTRACT

A bonded fibrous material is made by heating a fibrous structure in which some of the fibers are special composite fibers containing a potentially adhesive component. The composite fibers comprise at least two components, at least one of which is fiberforming and at least one of which is dispersed in the remainder of the components.

United States Patent [151 3,639,195 Sanders 1 1 Feb. 1, 1972 [54] BONDED FIBROUS MATERIALS AND [56] References Cited METHOD FOR MAKING THEM UNITED STATES PATENTS 7 Arthur Cwmb'am 3,442,140 5/1969 David ..156/306 x g'and 3,452,128 6/1969 Rains ..264/126 [73] Assignee: imperial Chemical Industries Limited,

Landon Enghmd FOREIGN PATENTS OR APPLICATIONS 22 Fil Sell, 13, 19 7 523,630 4; 1956 ganada ..264/126 946,4 9 1 1964 real Britain ..264/126 [21] 8,642 967,350 8/1964 Great Britain ..264/126 [30] Foreign Application Priority Data Primary Examiner-Lelar1d A. Sebastian Sept. 20, 1966 Great Britain ..41,8s9/66 Ammey-cushmam Darby 52 us. (:1 ..156/62.2, 156/626, 156/148, [571 ABSTRACT 156/ 181, 156/296, 156/306, 156/331, 161/72, A bonded fibrous material is made by heating a fibrous struc- [SU Int Cl B ture in which some of the fibers are special composite fibers [58} F1611! 0fsearch...:..::....156/622, 62.6, 148, 181, 296, cmtam'ng a pmem'ally adhesve The fibers comprise at least two components, at least one of which is fiber-forming and at least one of which is dispersed in the remainder of the components.

6 Claims, No Drawings BONDED FIBROUS MATERIALS AND METHOD FOR MAKING THEM This invention relates to methods for making bonded fibrous materials, which materials are bondedby the adhesive characteristics of fibers which constitute at least a proportion of the materials and to the bonded fibrous materials made by such methods.

It is known to form bonded fibrous materials from a mixture of at least two types of fiber, one type having a lower softening point than the other by applying, say, heat and, optionally, pressure to the mixture to cause the lower softening point fibers to become adhesive and thereby bond the material. However, such fibers may lose their fibrous form when treated in this way unless great care is taken in maintaining a critical temperature and the adhesive fibers may spread through the material and stiffen it to a degree which may detract from its utility in certain end uses. Materials which are bonded by application of an already nonfibrous adhesive binder material also suffer from this disadvantage and additionally uniform distribution of the binder is difficult to obtain.

To overcome these difficulties it has been proposed to employ, as binder fibers, composite artificial fibers of the multicomponent type. By multicomponent fibers in this case we mean staple fibers, flock fibers or continuous filaments comprising at least two fiber-forming polymeric components arranged in distinct zones across the cross section of filament, the number of zones being equal to the number of components and each zone being continuous along the length of the filament, and, so that these fibers can be used to bond fibrous materials, at least one component being capable of being rendered adhesive under conditions which leave the remainder unaffected. The multicomponent filaments can be prepared, for example by the methods described in British Patents Nos. 579,081, 580,764 and 580,941. The advantage of this type of fiber in bonding fibrous materials is that the adhesive component remains associated with the rest of the fibers, thus bonding the constituent fibers together only where the fibers are in contiguous relationship, and does not spread through the material.

The production of such fibers, however, involves complicated equipment for forming and bringing together the components in the correct proportions and the control of such equipment to produce fibers of consistent quality is very difficult.

Bonding of a similar nature to that produced by multicomponent filaments of the type described hereinbefore can be obtained by using, instead of multicomponent fibers, fibers, hereinafter for convenience and distinction being termed composite fibers, which consist of two or more components, at least one of which and preferably all of which are fiber-forming, in which at least one of the components is dispersed in the remainder.

Thus according to this invention there is provided a method for the manufacture of bonded fibrous materials which comprises forming a fibrous structure wholly or partly of composite fibers comprising at least two polymeric components, at least one of which and preferably all of which are fiber-forming, at least one of which components is dispersed in the remainder and at least one of which components is capable of being rendered adhesive by heat under conditions which leave the remainder unaffected and subjecting said structure to a heat treatment to render adhesive said component thus bonding the composite fibers to each other and to other fibers which may be present in the structure.

Composite fibers of the aforementioned type differ in structure from multicomponent fibers as hereinbefore defined in that each dispersed component is discontinuous along the length of the fiber and may occupy more than one zone across the cross section of the fiber and the term composite fibers includes staple fibers, flock fibers and continuous filaments. The production of such composite fibers does not involve the complicated equipment necessary to form continuous phases of the constituent components and keep them in fixed zones in each fiber. A component may be dispersed in the remainder of the fiber by any method involving the requisite degree of shearing action, starting with the constituents in liquid form or with one or all the constituents in solid form. When any of the constituents is in solid form, preliminary comminution may be advantageously employed. We have found it convenient when starting with the constituents in solid form, to mix together the individual constituents and then to effectmixing and spinning in a unit process by means of a conventional melt extruder.

In one aspect of our invention the composite fibers consist of only one polymeric component dispersed in one other although it is to be understood that more than one polymeric component could be dispersed in another or in a homogeneous blend of more than one component. It is essential that the component forming the continuousphase is fiber-forming and preferably both components should be fiber-forming. Any blend of immiscible polymeric components, one of which is fiber-forming, in which one component is capable of being rendered adhesive byheat without affecting the other component can be used to prepare the products of this invention and the relative proportions can vary over a wide range de pending on the degree of bonding, the strength of the fibers and the ease of processability required. Typical combinations although not limitative of the scope of this invention include dispersions of polyolefines in polyamides, dispersions of polyolefines inpolyesters and vice versa, dispersions of polyamides in polyesters and vice versa especially dispersions of poly(ethylene terephthalate) in poly(epsilon caprolactam) or poly(omega-amino-undecanoic acid) and dispersions of one polyamide in another, the two being mutually immiscible. Copolymers of any of the above can, of course, also be used often with advantageous results. Other constituents may also be present in the mixture, for example, pigments for delustring or changing the color of the fibers, optical brighteners, stabilizers and dispersing agents.

The component of the composite fibers to be rendered adhesive by the heat treatment may have a lower softening or melting point than the remainder of the fiber in which case the applied heat will be regulated so that only the lower softening or melting component is softened or melted and thus rendered adhesive. The heat treatment may be, for instance, a dry heat treatment using hot air, radiant heat or hot plates or rolls or, if the fibers are suitable, ultrasonic or dielectric treatment or may be, for instance, a steam or other hot fluid treatment.

However, the component to be rendered adhesive need not necessarily have a lower softening or melting point than the remainder of the fiber or may only have a lower softening or melting point under the particular heating conditions applied. Thus, for instance, the fibers may be such that the component to be renderedadhesive can be softened or melted by dielectric or ultrasonic means while the remainder of the fiber is unaffected by such treatment and in this case the adhesive componentneed not necessarily have a lower softening or melting point than the rest of the fiber. If, for instance, the heat treatment is a steam treatment, the fibers may be such that the component to be rendered adhesive may be plasticized and rendered adhesive while: the remainder of the fiber is unaffected and, in this case, the adhesive component need not have a lower softening or melting point than the remainder of the fibers under heating conditions other than the steam treatment.

Depending on the particular fibers used, the structure of the fibrous material, the particular heat treatment used and the properties desiredin the final product, it may be necessary to apply pressure to the materials during or shortly after the heat treatment and this may be accomplished for instance by pressing the materials between a pair of plates or rolls which may be heated and generally we have found that the application of pressure increases the strength of the bonded material.

The component which is rendered adhesive can be either the continuous phase or the dispersed phase. If the latter is to be rendered adhesive it is necessary that parts of the dispersed component break the surface of the composite fiber either on formation of the fibers or after receiving asuitable treatment. The component which has been rendered adhesive tends to remain associated with the remainder of the composite fiber rather than flow to other parts of the structure andform a film and hence the bonding is confined only to fiber-touching points thus ensuring the structure is not stiffened after bonding to a degree which will detract from its utility.

It is only necessary that the fibrous structure and the bonded textile material derived therefrom contain a small amount of composite fibers which are capable of bonding the structure although we prefer such composite fibers to be present in an amount of percent or more, and other fibers whichare inert to the heat treatment may be employed as a blend with such composite fibers. Depending upon the particular desiderata in the bonded textile material to be produced, the percentage of such composite fibers present in the fibrous web and the bonded textile material derived therefrom may be varied widely.

The composite fibers either in the form of continuous filaments or staple fiber including flock, may be associated with other fibers or continuous filaments of almost any sort, the only substantial limitation being that those other fibers must be inert to the activation treatment. Wool, silk, flax, cotton, regenerated cellulose, mineral fibers including asbestos and rock wool, glass fibers, synthetic polymeric fibers (for example, polyamide and polyethylene-terephthalate fibers), other composite fibers and the like are examples of such fibers which may in a particular instance be suitable. For the purpose of this specification and appended claims we term such fibers nonactivatable fibers.

The fibrous structures containing the composite fibers may be utilized in the textile art in numerous ways and the structures may take various forms depending upon the particular bonded textile material desired.

Thus, in the preparation of a woven or knitted fabric the composite fibers either alone or in admixture with nonactivatable fibers may be carded and then subjected to drafting and spinning to produce a yarn. The yarn after it has been woven or knitted is then subjected to a heat treatment which serves not only to stabilize the structure of the yarns within the woven or knitted fabric but also to stabilize the structure of the fabric as a whole by adhesion of fibers at points of intercrossing of the weft and warp or of loops in the knitted fabric. Such treatment may'conveniently be carried'out by passing the woven or knitted structure between the nip of a pair of heated rolls or by pressing it between heated platens. In continuous filament form the composite fibers may be fabricated into. cords by plying, after which the plies may be bonded together by heating under pressure. 1

Besides mixing fibers of relatively short lengths such as staple fibers in the manner contemplated in the descriptions hereinabove, the yarns may be formed of continuous filaments some or all of which are composite fibers and such yarns may be formed into woven or knitted or plied fabrics in the same manner as a staple fiber yarn.

Utilization of composite fibers in this manner affords textile fabrics of a knitted, woven or plied character wherein the tendency of the component yarns and filaments to slip with respect to the others is virtually eliminated. Knitted fabrics, for example, are thus free of any tendency to ladder when one of the knitted loops therein is broken.

Yarns consisting of or containing composite fibers and continuous composite filaments may be utilized in the manufacture of laid or woven scrims which are employed, for example, for the reinforcement of sheets of plastic. The use of compositefibers in the making of scrims greatly simplifies the manufacturing operation. For example, bonding of the laid or woven structure can be accomplished simply by the application of heat and pressure and thus the necessity for using a heat-sensitive warp size or dipping the structure in an adhesive before bonding on the loom is eliminated.

in a particularly useful embodiment of this invention the fibrous structures in the form of fibrous webs are employed in the production of nonwoven fabrics.

The fibrous web from which the nonwoven fabrics'are derived may be prepared by a variety of methods, and the method selected in a particular instance, depends to a very large extent on the length of the fibers when fibers other than continuous filaments are used.

Staple fiber webs may be prepared, for example, by a woolen or cotton carding machine or a garnetting machine which results in a web in which the staple fibers are oriented predominantly in one direction. The thin web obtained from a single card or garnet may be used by itself but sometimes it is necessary and desirable to superimpose a plurality of such webs to build up the web to a sufficient thickness and uniformity for the end use intended. ln building up such a web, alternate layers of carded webs may be disposed with their fiber orientation directions disposed at a certain angle, conveniently with respect to intervening layers. Such crosslaid webs have the advantage of possessing approximately the same strength in at least two directions. Furthermore cross lapping in this manner provides a product having a balanced stretchability. Random or isotropic staple fiber webs may be obtained, for example, by air-laying staple fibers. Thus, one

staple fiber web suitable for use in the process of this invention may be obtained by feeding continuous filaments to a cutter or breaker which discharges the fibers into an air stream produced by the blower. Suitable conduits are provided to guide a suspension of the staple fibers in a current of air to a foraminous surface on which the fibers settle as an interlaced and matted layer preferably being encouraged to do so by the application of suction on the other side of said surface. The foraminous surface can be in the form of an endless belt which is caused to travel past the place at which the fibers are fed to it, so as to form a continuous layer of indefinite length. Instead of having a travelling fiat screen, a stationary formed screen maybe used for the formation of shaped articles For example, it may take the form of a hat-shaped cone such as is used in the hatting trade. Alternatively, it may have any other form suitable for producing the desired shape of the bonded nonwoven fabric of this invention. A method of making a web containing fibers of a shorter length, say 0.5 inches or shorter, involves a wet laying technique such as use of a Fourdrinier or other papermaking machine.

Continuous filament webs of composite filaments may conveniently be prepared by drawing off directly from a spinning i.e., polymer extrusion) unit, usually as a bundle of filaments, or they may be formed from a package or other storage device for yarn (multifilaments) or monofilament already spun. Thus the filaments (mono or multi) may be formed into a layered web by feeding them onto a collecting surface where they accumulate in overlapping layers, the individual filaments in each layer being predominately coplanar, lying parallel or substantially parallel to the collecting surface and to the bottom and top of the web so formed.

Conveniently, the step of web formation is accomplished by mechanical means, such as forwarding jets, which may be operated to lay the filaments down at random or in some desired pattern. The collecting surface may be rotated or oscillate to produce even accumulation of the filaments and a moving belt may be used as the collecting surface and in one embodiment of this invention described more fully hereinafter the continuous filament web is laid directly onto a moving belt.

If desired the fibrous web may be needle-punched on a conventional needle loom with or without a nonwoven scrim.

The invention will now be described in more detail with reference to the following examples which are in no way intended to limit the scope thereof.

EXAMPLE I Composite filaments were melt spun from an intimate blend of 70 percent poly(epsilon-caprolactam) and 30 percent poly(ethylene terephthalate) and drawn and cut to give fibers of 3.5 denier and 2.5-inch staple length. The composite fibers were then blended with 3 denier 2.5-inch poly(hexamethylene union 1 n1 adipamide) fibers in the proportions of percent to 75 per cent respectively and the blend was carded in a Shirley miniature carder. Two laps of the carded blend were cross-lapped and the fibrous structure so formed was placed in a hydraulically operated press having heated plates and hot pressed at a temperature of 215 C. and a pressure of 200 p.s.i. The heat treatment rendered the poly(epsilon caprolactam) component of the composite fibers adhesive without affecting the remainder of the fibers and the adhesive bonded the structure together at fiber crossover points giving a strong yet pliable and drapable nonwoven fabric in which there was no evidence of spread of the poly (epsilon-caprolactam) adhesive through its structure with its concomitant adverse effects on fabric properties. The tensile strength of the fabric was measured in lnstron (Registered Trademark tensile-testing machine by extending strips of the fabric 1 inch wide and 5 cm. long at a rate of 5 cmjmin. and the product was found to have an average breaking strength of 450 Kg./g./cm. at an average extension at break of 24.3 percent.

EXAMPLE 2 Example 1 was repeated except that the composite fibers and the poly(hexamethylene adipamide) fibers were blended in the proportions of 50 percent to 50 percent. The product was again a well-bonded yet pliable and drapable nonwoven fabric bonded through the agency of the poly(epsilon-caprolactam) component of the composite fibers having an average tensile strength of 380 Kg./g./cm. and an average extension of break of 21 percent.

EXAMPLE 3 Example 1 was repeated except that the composite fibers and the poly(hexamethylene adipamide) fibers were blended in the proportion of 75 percent to 25 percent respectively. The product was again a well-bonded yet pliable and drapable nonwoven fabric bonded through the agency of the poly(epsilon-caprolactam) component of the composite fibers having an average tensile strength of 354 Kg./g./cm. and an average extension at break of 20 percent.

EXAMPLE 4 Example I was repeated except that the composite fibers used were spun from an intimate blend of 40 percent poly(ethylene terephthalate) and 60 percent poly(omegaamino undecanoic acid). The product was again a strong yet pliable and drapable nonwoven fabric.

What we claim is: 1

l. A method for the manufacture of bonded fibrous materials which comprises forming a fibrous structure at least partly of composite fibers, each composite fiber comprising at least two polymeric components, at least one of which is dispersed as a discontinuous phase within a continuous phase defined by at least one other component, at least the component defining the continuous phase being a fiber-forming component and at least one, but not all, of which components is capable of being rendered adhesive by heat under conditions which leave the remainder unaffected, and subjecting such fibrous structure to a heat treatment to render adhesive and adhesive component thus bonding the composite fibers to each other and to other fibers which may be present in the structure.

2. A method as claimed in claim I in which the heat treatment is accompanied by the application of pressure.

3. A method as claimed in claim 2 in which the treatment comprises pressing the structure between heated rolls or plates.

4. A method as claimed in claim 1 in which said composite fibers consist of poly(epsilon-caprolactam) and poly( ethylene terephthalate).

5. A method as claimed in claim 1 in which said composite fibers consist of poly(omega-amino undecanoic acid) and poly(ethylene terephthalate).

6. A method as in claim ll wherein the dispersed component is a fiber-forming polym eric co rnpo nen t. 

2. A method as claimed in claim 1 in which the heat treatment is accompanied by the application of pressure.
 3. A method as claimed in claim 2 in which the treatment comprises pressing the structure between heated rolls or plates.
 4. A method as claimed in claim 1 in which said composite fibers consist of poly(epsilon-caprolactam) and poly(ethylene terephthalate).
 5. A method as claimed in claim 1 in which said composite fibers consist of poly(omega-amino undecanoic acid) and poly(ethylene terephthalate).
 6. A method as in claim 1 wherein the dispersed component is a fiber-forming polymeric component. 